1. Field of Invention
The present invention relates to a semiconductor light emitting device with thick metal layers.
2. Description of Related Art
Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes such as surface-emitting lasers (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
FIG. 1 illustrates an LED including large area metal-to-metal interconnects, described in more detail in U.S. Pat. No. 7,348,212. The structure illustrated in FIG. 1 includes a flip chip light emitting device attached to a mount 70. The flip chip device includes a substrate 73 attached to semiconductor device layers 74, which include at least one light emitting or active layer disposed between an n-type region and a p-type region. N-type contact 71 and p-type contact 72 are electrically connected to the n- and p-type regions of semiconductor structure 74. Thin metal layers 76a and 77a are formed on contacts 71 and 72, and thin metal layers 76b and 77b are formed on mount 70. Thick ductile metal layers 78 and 79 are plated on either mount 70 or contacts 71 and 72, thus on either regions 76a and 77a or regions 76b and 77b. Metal layers 78 and 79 are selected to be ductile, have high thermal and electrical conductivity, and be reasonably resistant to oxidation. For example, metal layers 78 and 79 may be Au, which has good thermal conductivity; Cu, which has even better thermal conductivity than Au; Ni; or Al, which is less expensive than Au or Cu. Metal layers 78 and 79 may be between one and 50 microns thick and are often between 5 and 20 microns thick.